Field of the Invention
The invention relates to a method for creating a magnetic resonance spectroscopy data record for a volume of interest using a magnetic resonance unit with at least two RF reception coils, and a method for determining a complex sensitivity factor of an RF reception coil, which is part of an arrangement made up of a number of RF reception coils.
The invention also concerns a magnetic resonance apparatus, which is configured to execute the method, as well as a non-transitory, computer-readable data storage medium encoded with programming instructions for implementing such a method.
Description of the Prior Art
In magnetic resonance tomography (MRT) it is frequently advantageous not to acquire the MR signal using a large radio-frequency (RF) receive coil but using an arrangement—also referred to as an array or phased array—composed of a number of RF reception coils. These can often be arranged directly on the body of the patient and therefore have a high signal to noise ratio (SNR). Combining the signals acquired simultaneously by the different array coils to form a composite signal is not simple, however, because the process has to take into account the different sensitivity profiles of the individual coils in order to compensate for spatial intensity variations. With magnetic resonance spectroscopy (MRS) it is important to weight the contributions of the individual coils with the correct sensitivity factor for each voxel, because otherwise the SNR suffers, and spectra from different voxels cannot be compared, so it is impossible to ascertain any spatial variation in the concentration of metabolites. The sensitivity profiles of the coil arrangements should be calculated anew in each instance before a measurement on the patient, because they can vary significantly due to the individual positioning of the coil arrangement on the patient.
Different approaches are known for calculating the sensitivity profiles of the individual coil elements of an arrangement composed of RF reception coils. In the article by M. A. Brown “Time Domain Combination of MR Spectroscopy Data Acquired Using Phased-Array Coils”, Magnetic Resonance in Medicine, 52:1207-1213 (2004) a method is described in which the first point of the free induction decays (FIDs) of the signals acquired with the different RF coils is used and the sensitivity factors are calculated therefrom. However this method produces flawed results when the spectra are very noisy.
In the article by T. Schäffter, P. Börnert et al. “Fast 1H Spectroscopic Imaging Using a Multi-Element Head-Coil Array”, Magnetic Resonance in Medicine, 40:185-193 (1998) a method is described in which the sensitivity profiles are calculated by means of a set of calibration images, which is acquired using both the coil arrangement and the body coil serving as reference. However, this requires prior measurement.
C. T. Rodgers and M. D. Robson in “Receive Array Magnetic Resonance Spectroscopy: Whitened Singular Value Decomposition (WSVD) Gives Optimal Bayesian Solution”, Magnetic Resonance in Medicine, 63:881-891 (2010) propose a singular value decomposition (SVD) to determine the complex sensitivities. This approach is relatively complex.